Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $185.92   12.267%   $208.7268   $208.73   $208.75   $208.70  
  Purchase #2 $84.55   10.644%   $93.5495   $93.55   $93.55   $93.50  
  Purchase #3 $77.63   8.809%   $84.4684   $84.47   $84.45   $84.50  
  Purchase #4 $73.83   3.663%   $76.5344   $76.53   $76.55   $76.50  
  Purchase #5 $201.27   7.308%   $215.9788   $215.98   $216.00   $216.00  
  Purchase #6 $22.78   11.338%   $25.3628   $25.36   $25.35   $25.40  
  Purchase #7 $62.49   11.645%   $69.767   $69.77   $69.75   $69.80  
  7 purchase totals = $708.47       $774.3877   $774.39   $774.40   $774.40